The present invention relates to a CATV terminal unit disposed within a subscriber's house to receive a CATV broadcast.
In the CATV, a signal is transmitted via a transmission line such as a coaxial cable, etc., and its transmission band is divided into a number of channels which are efficiently used so as not to produce empty channels, and thus a video signal and an audio signal are transmitted. The normal television receiver cannot receive all the television programs transmitted thereto. Therefore, in the CATV, it is necessary to provide a terminal unit having a channel converter functions to receive channels which cannot be directly received by the television receiver. The terminal unit correspondingly has a function for selecting a designated channel.
The broadcast of the programs transmitted by the CATV is generally classified into a "rebroadcast" for transmitting broadcast programs as they are, and an original independent "broadcast" produced by a system operator. In the case of the independent broadcast, there is a "pay-channel" in which an additional charge must be paid every month, and there is a "pay-per-view channel" in which a charge is set every program. A subscriber of the CATV selects programs he wants to receive, makes an application for those programs and pays the charge corresponding to the service every month. Namely, there are channels receivable and non-receivable for only a basic charge. Since a signal of the chargeable channel is also transmitted by a common coaxial cable, it is necessary to take measures in which the subscriber paying only for the basic charge cannot receive this signal.
Therefore, a scrambling operation is performed with respect to the chargeable channels and only a descrambler of a terminal unit of an admitted subscriber is operated so that the scrambled signal is thereby returned to its original state.
These subscribers are discriminated by individually controlling the terminal units disposed within the houses of the respective subscribers by data from a broadcasting center. Therefore, each of the terminal units has a function for receiving this data and has recognition numbers such as addresses, ID numbers therein which are proper to the respective terminals.
Recently, another CATV terminal unit has been proposed. In this terminal unit, the operations such as the channel setting of the above channel converter and the turning-on-and-off of the electric power is controlled by not only the operation of an operating keyboard but also by a wireless remote controller. Further, an outlet for television power is disposed through a switch which is turned on and off in association with the turning-on and turning-off operations of the electric power of the terminal unit. The electric power is supplied to the television receiver from the outlet for television power. In such a construction, the power of the television is also simultaneously turned on and off by the operation of the wireless remote controller of the terminal unit, which is a convenient feature. However, such a conventional terminal unit has no sound volume changer, and therefore the sound volume is only adjusted by the operation of the sound volume changer (mechanical or electronic) of the television receiver, which is cumbersome in operation.
Accordingly, it has further been considered that the sound volume changer be disposed in the terminal unit, and in addition to the turning-on-and-off of electric power and the channel selection, the sound volume adjustment is also controlled by the wireless remote controller of the terminal unit. In such a construction, under the condition that the sound volume changer of the CATV terminal unit is set to a maximum value the sound volume changer of the television receiver is fixed to a maximum value at the ordinary watching situation of the television. In actual use the sound volume is adjusted by using the sound volume changer of the CATV terminal unit without using the sound volume changer of the television receiver.
In the CATV terminal unit having the sound volume adjusting function mentioned above, as shown in FIG. 1, a video recording apparatus 3 is sometimes connected between a CATV terminal unit 1 and a television receiver 2 and is used in this connecting state. In such a case, when a program of the CATV broadcast received by a terminal unit is recorded by the video recording apparatus 3, and the sound volume of the CATV terminal unit 1 is set to a low value or is in a mute state, only the picture image, that is, a picture image without sound is recorded to the video recording apparatus 3. When a person notices this state during the recording operation, the person can either increase the sound volume or release the mute state so as not to record the picture image without sound. However, when the so-called "absence recording" is performed by using a program timer function of the CATV terminal unit 1 and a timer function of the video recording apparatus 3, the picture image without sound might be recorded since there is no one watching the television receiver to notice this state.